Sometimes a caching/cookie issue can cause the Microsoft website to show this error thinking you are not logged in.
To negate this you can open a private/incognito browsing session in your web browser (instructions below for the most common browsers), log in to your Microsoft account again and attempt the redemption.
Click More New Incognito Window.
A new window appears. In the top corner, check for the Incognito icon .
Click the menu button and then click New Private Window.
Click Settings and more > New InPrivate window.
In the Safari app on your Mac, click File > New Private Window, or switch to a private window that’s already open.
Click and click Private mode.
Go to the Vivaldi menu > File > New Private Window.